As the price of the conventional a-Si (amorphous silicon) TFT (thin film transistor) LCD (liquid crystal display) keeps going down and the applications of the LTPS-TFT (low temperature polycrystalline silicon thin film transistor) in small-size display is extending day by day, the LTPS-TFT has gained its market share in mobile terminal devices, such as personal digital assistant, digital camera, cell phone, etc., because of its advantage on resolution, brightness, size and electromagnetic disturbance.
However, on producing the LTPS-TFT by laser annealing, the active layer of the transistor is formed after the laser recrystallization of the a-Si film, so that the resulting silicon grain structure would be limited in size owing to the thickness of the film. And the silicon grains with irregular sizes are spread in the active layer of the transistor, which causes the differences in the electric properties of the components and so diminishes the uniformity. But, on the contrary, if the active layer of transistor is formed ‘before’ the laser recrystallization of the a-Si film, a surface tension induced shrinkage would happen on the active layer owing to the melting of the whole silicon film. Therefore, the conventional method can not be used in fabricating LTPS-TFTs.
In addition, the structure of the components, like TFT and silicon-on-insulator metal oxide semiconductor field effect transistor (SOI-MOSFET), would comprise an insulated layer with poor thermo conductivity under active layer. When the working current of the device is large, the temperature of the active layer would suddenly rise and the mobility of the carrier in the active layer would be diminished. So, a related technique suggests that the bigger channel W can be divided into a plurality of smaller channels Wi connected in a parallel way to overcome the self-heating effect. As shown in FIG. 7, it is a view showing the way to overcome the self-heating effect according to the prior art.